Glyphosate affects persistence and tolerance but not antibiotic resistance

Glyphosate is a herbicide widely used in food production that blocks the synthesis of aromatic amino acids in plants and in microorganisms and also induces the accumulation of the alarmone (p)ppGpp. The purpose of this study was to investigate whether glyphosate affects the resistance, tolerance or persistence of bacteria towards three different classes of antibiotics and the possible role of (p)ppGpp in this activity. Glyphosate did not affect the minimum inhibitory concentration of the tested antibiotics, but enhanced bacterial tolerance and/or persistence towards them. The upshift in ciprofloxacin and kanamycin tolerance was partially dependent on the presence of relA that promotes (p)ppGpp accumulation in response to glyphosate. Conversely, the strong increase in ampicillin tolerance caused by glyphosate was independent of relA. We conclude that by inducing aromatic amino acid starvation glyphosate contributes to the temporary increase in E. coli tolerance or persistence, but does not affect antibiotic resistance.

Automated summary

This study investigated the effects of glyphosate on the resistance, tolerance, or persistence of bacteria towards antibiotics, as well as the role of (p)ppGpp in this process. The results showed that glyphosate did not affect the minimum inhibitory concentration of tested antibiotics, but it enhanced bacterial tolerance and/or persistence towards them. The increase in ciprofloxacin and kanamycin tolerance was partially dependent on the presence of relA, while the strong increase in ampicillin tolerance caused by glyphosate was independent of relA. The study concluded that glyphosate contributes to the temporary increase in E. coli tolerance or persistence by inducing aromatic amino acid starvation, but does not affect antibiotic resistance.